Attempting to use B pistons in a 12 valve block. The 12 valve has a different angle and the reliefs will have to be adjusted and I'm trying to judge how much before I buy.

 

either way, you're better off just claying it. a comment from (even a well-intending and very knowledgeable) stranger on the internet is no substitute for good engine building practice.

whenever you're fitting non-standard pistons (anything other than the original part number) into an engine, you clay them to check the piston to valve clearance. don't short cut it.